(1) Field of the Invention
The present invention relates to a method for producing a semiconductor device, more particularly to a method for producing a complementary metal-insulator-semiconductor (MIS) type integrated circuit device (IC) having general-purpose output stages.
(2) Description of the Prior Art
Rather than manufacture specialized IC's for each order from a customer, it is well known to manufacture a general-purpose IC and then customize it to the desired functions. Specifically, general-purpose IC's are produced in advance up to the diffusion process step by a common pattern, and are later customized have specific functions by employing various masking processes. This technique, known as the master slice process, enables significant reductions in design time and labor and in manufacturing costs as well as speedier delivery to customers.
Customization is usually effected either by first forming common contact windows on the general-purpose IC and then forming specific wiring patterns by using of different wiring masks or by forming specific contact window patterns by using of different contact window masks and then forming common wiring patterns.
Now, a complementary MIS IC such as a microcomputer includes a number of logic circuits. Some of the logic circuits have output circuits. In each output circuit, the final output-stage transistor is designed to be either an N-channel open-drain output type, i.e., a type in which current flows out from an output pad, or a P-channel open-drain output type, i.e., a type in which current flows into an output pad.
Depending on whether an N-channel or a P-channel open-drain type is required, it has sometimes it is necessary in conventional processes to change the mask to form the desired diffusion region in the final output-stage transistor.